Adjustable coupling device and monitoring means therefor



Nov- 5 H. E. OVERACKER ETAL 2,724,799

ADJUSTABLE COUPLING DEVICE AND MONITORING MEANS THEREFOR Filed May 16, 1950 2 Sheets-Sheet 1 I N V EN TORS Horace E Overacker By MY/iam 1?. He /e/f 22, 1955 H. E. OVERACKER ET AL ,7

ADJUSTABLE COUPLING DEVICE AND MONITORING MEANS THEREFOR Filed May 16, 1950 2 Sheets-Sheet 2 r Ska Mae Ta mfi Vv m m 5 A? 6 WW v. B 7 E 1 l 9 /F J m. ,W 2 6% M "m v u 7 w w J( m H i A v a 7M 7 H H 6 0 89 6 3 W 2 1. 0 7. 3 /l 1111 11 I a y, 32%

ATTOR/VE Y5 United States Patent ADJUSTABLE COUPLING DEVKCE AND MONITORWG MEANS THEREFGR Horace E. OveraclrenLos Altos, and William R. Hewlett, Palo Alto, Calif., assignors to Hewlett-Packard (10m puny, Palo Alto, Calif., a corporation of California Application May 16, 1950, Serial No. 162,374

3 (Ilairns. (Cl. 324-95) This invention relates generally to high frequency electrical apparatus suitable for signalling or test purposes, and capable of adjustment to supply high frequency energy at a plurality of power levels.

So-called attenuators have been commonly used in the past for adjusting the energy transfer from a high frequency generator to an antenna system or other load. Attenuators of the mutual inductive coupling type employ a pickup inductance or loop which is connected to the load, and which can be adjusted to a selected position with respect to an inductance element forming part of the generator. It is possible to calibrate such an a tenuator whereby for a given performance of the generator the position of the attenuator pickup loop corresponds to a predetermined power output. However with the conventional methods employed it has been difficult to quicklydetermine deviations from calibrated values and to make correcting adjustments. In addition prior attenuators have had the inherent defect that the impedance of the feed line connecting the attenuator with the load is not matched with the impedance of the pickup loop, for various frequencies of operation.

It is an object of the present invention to provide improvement in apparatusof the above character which will facilitate accurate calibration of an attenuator of the mutual inductive coupling type, and to facilitate making correcting adjustments to insure the desired accuracy after calibration.

A further object of the invention is to provide an attenuator of the mutual inductive coupling type for transferring energy from high frequency generators to a load, and which incorporates novel means for matching the impedance of the pickup loop with the impedance of the feed line which connects the attenuator to a load.

Another object of the invention is to provide improved attenuator and monitoring means of the type described above having a novel arrangement of pickup loops which will afiord a high degree of stability and accuracy.

" Additional objects and features of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawing.

Referring to the drawing Figure 1 is a plan view, partly in section, illustrating equipment incorporated in the present invention.

Figure 2 is a cross-sectional detail taken along the line 22 of Figure 1.

- Figure 3 is a cross-sectional detail taken along the line 33 of Figure 1.

Figure 4 is a cross-sectional detail taken along the line 44 of Figure 1.

Figure 5 is an enlarged cross-sectional detail taken along the line 5-5 of Figure 1.

Figure 6 is an enlarged detail, partly in cross-section, illustrating the adjustable plunger part of the apparatus, and which forms the mounting for the attenuator pickup conductor.

2,724,799 Patented Nov. 22, 1955 Figure 7 is a view taken along the line 77 of Figure 6.

Figure 8 is a schematic view illustrating the various essential parts of the apparatus.

Figure 9 is another schematic view taken along the line 9-9 of Figure 8.

Our invention can be best understood by first referring to Figures 8 and 9. An inductance coil 10 is represented as a part of a high frequency oscillation generator 11. By high frequency generator we have particular reference to frequencies of operation of the order of from 10 to 500 megacycles. The inductance 10 should be so rleated to the circuit of the generator that it may supply power to a load. As is well known to those familiar with high frequency generating equipment operating in the frequency range mentioned, the generator may for example consist of an oscillator of the electronic type, coupled to an electronic amplifier. The permissible power output of such a generator can be adjusted for example by. varying the biasing voltage supplied to the vacuum tube of the amplifier.

A grounded metal shield tube 12 is disposed in fixed relation to the inductance 1t}. Slidably disposed within the tube 12 there is a plunger-like device 13, which includes the tube 14 and the metal plug member 15. Spring metal contact fingers 16 are carried by the periphcry of the member to establish continuous good elec with respect to the shield tube 12, and at right angles to the axis of the same. One end of the pickup loop 17 is grounded by connecting the same to member 15, and the other end is connected to a compensating network including the resistors 13 and 1?, and the condenser 20. A feed line 21 serves to connect the compensating network with a load, such as an antenna system or the like. This feed line can be of the coaxial type, including the outerand inner conductors 22 and 23. That part of the outer conductor 22 near the member 15 can be in the form of a metal tube as illustrated. The center conductor 23 connects to the compensating network at a point between the resistors 18 and 19 as illustrated.

By proper selection of the values for resistors 18, 19 and for condenser 20 the compensating network serves to matchv the impedance of the pickup conductor 17, with the impedance of the feed line 21. In other words, the compensating network is such that at the point of connection with the feed line 21, the characteristic impedance is the same looking in either direction. That is, the impedance from the compensating network into the feed line is the same as the impedance from the feed line looking into the compensating network. This network automatically compensates for changes in frequency, because as the frequency of operation increases, the impedance of the frequency branch formed byresistor 18 with loop 17 increases, while the impedance of the other branch formed by. resistor 19 and condenser 20, decreases. Thus for any selected frequency of operation, the impedance matching makes for most efficient transfer of energy from the pickup conductor 17 to the feed line 21.

In addition to the above we provide a pair of monitoring pickup loops in the form of linear wires or condoctors 26 (Figure 9) which serve to pick up energy for monitoring purposes. conductors are grounded, and the other ends are connected together and to the detecting circuit 27. As viewed in Figure 9 the conductors 26 are spaced equal distances from the axis of the shield tube 12, so that when the conductor 17 is advanced to a position between Corresponding ends of these.

3 the conductors 26, it is disposed midway between the same as illustrated in Figure 9.

The detecting circuit 27 can be the same as commonly used with high frequency monitoring circuits. Thus it is shown including the inductance 28, detector 29, resistor 30 and condenser 31. The detector can be a crystal type rectifier. Rectified components from the detecting circuit 27 are supplied to suitable indicating means, such as the meter 32, which is in series with resistor 33.

For suitable operation at frequencies ranging from to 500 megacycles, the values employed for the various electrical elements can be as follows: Pickup conductor 17, 1 inch in length and linear; pickup conductors 26, 1% inches in length and linear; resistors 18 and 19, each 50 ohms; condenser 20, 8 mfd.; inductance 29, about 1 microhenry; rectifier 29, one of the crystal type known by manufacturers specifications as No. G7; resistor, 30, 100 ohms; condenser 31, .0001 mfd.; resistor 33, 30 k.; and the indicating meter 32 a visual reading micrometer.

Assuming a given frequency of operation, one may calibrate the apparatus whereby for a given position of the pickup conductor 17, a predetermined amount of power is supplied to the output. For each calibrated position of the pickup conductor 17, the meter 32 will have the same reading. After such calibration the operator positions the pickup conductor 17 according to the power required for the load. For a selected calibrated position the meter 32 is checked to assure proper operation. If the meter 32 does not read to zero-set value, which is the value determined during calibration, then meter 32 is brought to the zero-set value by adjustment of bias voltage on the vacuum tube of the amplifier. While such corrective adjustments are being made one can check with the meter 32 to determine when operation of the apparatus has been returned to that prevailing at the time of calibration. Assuming that the high frequency generator is one which can be adjusted to operate on any one of a plurality of selected frequencies, within a predetermined frequency range, the pickup conductor 17 will continue to efliciently transfer energy to the feed line 21 and to the load for any one of the selected frequencies. In addition the apparatus can be calibrated as previously explained, for each of the selected frequencies.

The monitoring means is made relatively accurate because of the use of two pickup conductors 26, and because of the symmetrical positioning as illustrated. Thus for any selected position of the movable pickup conductor 17, the distance between the same and conductors 26 remains the same. Thus the capacitance values between each of the conductors 26 and the conductor 17 remain equal and both the electrostatic and electromagnetic fields of the conductor 17 remain symmetrical at all times. The conductor 17 may be moved to positions either in front of or behind the conductors 26.

Figures 1 to 7 inclusive illustrate a specific form of apparatus incorporating features of the invention described above. The shield tube 12 is fixed to and extends through one wall of a box-like chassis 36. The plunger-like device 13 is similar in general construction to that illustrated diagrammatically in Figure 8. The pickup conductor 17 is in the form of a relatively stiif wire, the ends of which are attached to the metal studs or posts 37 and 38. The posts are attached to the ends of a card 39 of insulating material, and the one post 38 is anchored to the member 15. The resistor 18 is connected between the post 37 and a terminal eyelet 41, which likewise connects with the central conductor 23. The resistor 19 and the condenser 20 are connected in series between the eyelet 41 and member 15. A flexible coaxial cable 42 is shown connected to the end of tube 22 and to the central conductor 23, to form an extension of the general feed line 21.

As suitable means for adjusting the plunger-like device 13 longitudinally of the shield tube 12, we have shown a rotatable shaft 43 which is journaled at one end on the chassis 36, and at its other end by a bracket 44 which is carried by the adjacent end of the shield tube 12. Pulleys 46 and 47 are secured to the shafts 43, and are engaged by the end portions of the operating cord or cable 48. This cable is guided over the pulleys 49 and 51, and its end portions are secured to the pulleys 46 and 47, and are wrapped about the peripheries of the same in opposite directions whereby when the shaft 43 is rotated, the cable moves in one direction or the other longitudinally of the tube 12. A stud 52 is attached to one side of the tube 14, and is accommodated in a longitudinal slot 53 formed in tube 12 (Figure 5). This stud is slotted to receive the cord 48 and is threaded to receive the clamping nut 54. Thus the tube 14 can be attached to the cord 48 to enable one to position the device 13 at any point along the length of the tube 12, by rotation of the shaft 43.

As suitable means for operating the shaft 43 we have shown another shaft 56 which extends through the chassis 36 parallel to shaft 43, and which carries a gear 57 which engages a gear 58 mounted upon shaft 43. One end of the shaft 56 is shown extending through the instrument panel 59, where it is provided with the operating knob 61 and a calibrated dial. By turning this knob the device 13 can be positioned as desired along the length of the tube 12.

The monitoring pickup conductors 26 are shown extended across the end of the tube 12, the same as illustrated in Figures 8 and 9. A housing 62 is shown for enclosing the choke 28, a crystal rectifier 29, and the condenser 31.

Within the chassis 36 there is a rotatable turret-like coil support 63 which has a plurality of arms 64, each of which serves to support an inductance coil 66. The coils connect with switch contacts 67, which in turn are adapted to be brought into engagement with stationary switch contacts 68. In this manner a particular coil is operatively connected with the associated high frequency generating means, and when a particular coil is connected it is in symmetrical and inductive relation with the pickup conductors. The coils have different values of inductance and serve to determine the frequency of operation of the high frequency generator.

As suitable means for turning the coil support 63 to a desired position, it is shown carried by a tubular shaft 71 which is rotatably carried by the shaft 56. Gear 72 mounted upon shaft 71 engages a gear 73 which is mounted upon the adjacent parallel shaft 74. Shaft 74 extends through the instrument panel 59 and is there provided with the operating knob 76.

It will be evident from the foregoing that the apparatus illustrated in Figures 1 to 7 inclusive incorporates all of the features diagrammatically illustrated in Figures 8 and 9. By turning knob 76 an operator can select a desired frequency of operation. By turning the knob 61 it is possible to adjust the amount of attenuation and thus adjust the power supplied to the load to a desired level which is marked on meter 32. The output can then be read directly from the calibrated dial.

We claim:

1. In high frequency electrical apparatus of the type having generating means for supplying high frequency energy to a load, the generator including an inductance element to which an output can be coupled, a grounded metal shield tube having one end of the same disposed adjacent said element, a plunger-like device slidably disposed in said tube, a substantially linear pickup loop carried by said device and extending diametrically of the tube and at right angles to the axis thereof, said pickup loop being adapted to have mutual inductive coupling to said inductance element, the value of said coupling be ing adjustable by adjusting the position of said device,

a feed line attached to the device and adapted to supply high frequency energy to a load, a matching impedance network serving to connect said pickup loop to said feed line for effective transfer of high frequency energy, and monitoring means for indicating the amount of energy transferred to the output, said monitoring means comprising a pair of monitoring pickup loops extending across said end of the shield tube and parallel to said first named pickup loop, said monitoring pickup loops being disposed symmetrically on opposite sides of the axis of the shield tube and being equidistant with respect to the first named pickup loop, energy detecting means connected to said monitoring pickup loops, and energy indicating means connected to the detecting means.

2. In high frequency electrical apparatus of the type having generating means for supplying high frequency energy to a load, the generator including an inductance element to which an output can be coupled, a grounded metal shield tube having one end of the same disposed adjacent said element, a plunger-like device slidably disposed in said tube, a substantially linear pickup loop carried by said device and adapted to have mutually inductive coupling with said inductance element, the value of said coupling being'adjustable by adjusting the position of the plunger-like device in the shield tube, a feed line attached to the device and adapted to supply high frequency energy to a load, and a matching impedance network serving to connect said pickup loop to said feed line for effective transfer of high frequency energy, said impedance network providing two branches, one including the pickup loop in series with a resistance and the other including a resistance in series with a condenser, the point between said branches being connected to the feed line, said matching impedance network serving to automatically compensate for changes in frequency of operation.

3. In high frequency electrical apparatus of the type having generating means for supplying high frequency energy to a load, the generator including an inductive element to which an output can be coupled, a ground metal shield tube having one end of the same disposed adjacent said element, and normally in fixed spaced relationship thereto, means slidably disposed within said shield tube for transfer of high frequency energy from said inductance element to a load, said last means including a pickup loop having mutual inductive coupling to said first named element, and monitoring means for indicating the power transferred to the load, said monitoring means including two side by side and laterally spaced pickup loops each extending across said end of shield tube and symmetrically disposed on opposite sides of the axis of the same and equidistant with respect to the first named pickup loop, said two side by side and laterally spaced pickup loops being stationary relative to the tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,204,179 George June 11, 1940 2,296,678 Linder Sept. 22, 1942 2,419,984 Boothroyd May 6, 1947 2,474,795 Van Beuren June 28, 1949 2,475,344 Wheeler July 5, 1949 2,579,751 Muchmore Dec. 25, 1951 2,589,843 Montgomery Mar. 18, 1952 FOREIGN PATENTS 616,226 Great Britain Jan. 18, 1949 

